feat(alerts): 新增客户集中度预警规则 customer_concentration + 预测偏差规则启用/联动每日预警生成

- alert_rules: 新增 rule_type=customer_concentration（单一/前N客户收入占比超阈值触发，黄=超阈值/红=阈值x倍数）
  数据源 zxt_masterbill 客户(往来单位)收入聚合，unit_id<=0 占位剔除；无客户数据可回退 KPI 口径
  复用现有 KPIAlert 生成链路：check-all 内联分支 + 专用端点 POST /run-customer-concentration
- alert_generator(每日9:00): 新增规则引擎步骤，复用上述检查函数跑 forecast_deviation/customer_concentration
- AlertList.vue: 规则类型筛选/编辑项 + 参数表单 + 客户集中度检查按钮
- 测试: tests/test_customer_concentration_rule.py 17 条（规则注册/聚合/双数据源/黄红灯/去重/check-all）
- 验证脚本: scripts/verify_forecast_deviation_rules_e2e.py / verify_customer_concentration_rule_e2e.py

frontend/src/api/index.ts

@@ -172,6 +172,8 @@ export const alertRulesApi = {
   dynamicThresholds: (params?: any) => api.get('/alert-rules/dynamic-thresholds', { params }),
   // AI事前预警
   checkForecast: () => api.post('/alert-rules/check-forecast'),
+  checkForecastDeviation: () => api.post('/alert-rules/run-forecast-deviation'),
+  checkConcentration: () => api.post('/alert-rules/run-customer-concentration'),
   generateSuggestions: () => api.post('/alert-rules/generate-suggestions'),
 }